This invention relates to a pump for a fuel injection system, and more particularly to an improve high pressure fuel injection pump.
It has been well known that the fuel efficiency, performance and emission control of an engine can be improved by use of a fuel injection system. With such systems, fuel is delivered under pressure to the engine through a fuel injector which generally includes an injection valve that is opened and closed so as to permit the fuel to be sprayed to the engine. The fuel may be introduced either to the induction system or directly into the combustion chambers of the engine.
Although this type of arrangement has a number of advantages, there are areas where performance can still further be improved. For example, it is normally the practice to supply the fuel to the fuel injectors by means of a high pressure pump. Such pumps are conventionally reciprocating type pumps and in some instances, there may be employed one pump for each fuel injector. The pumps may, however, include a common driving element. The disadvantage with this type of construction is that the output pressure of the fuel from the reciprocating pump varies during the pumping cycle. Basically, the pressure variations are approximately equal to the variations in speed of the pumping piston. These pressure variations can, therefore, cause problems in conjunction with the accurate metering of the fuel. Also, with this type of system, it has been the practice to have the injection pump operate so that its pump cycle is related to the timing of the opening of the injector valve. This compromises the pump design and also has other disadvantages.
To overcome the effect of these pressure pulses, it has been proposed to deliver the fuel from the high pressure pump to an accumulator chamber and then to the fuel injector. The use of accumulator chambers can provide some damping in the pressure variation. However, even if accumulator chambers are employed, the pressure pulses generated by the pump still can travel through the system and cause problems with accurate fuel metering.
It is, therefore, a principal object of this invention to provide an improved pump for a fuel injection system for an engine.
It is a further object of this invention to provide a fuel injection pump for an engine wherein the pressure output pulses from the pump are substantially minimized.
It is a further object of this invention to provide a multiple piston fuel injection pump for an engine wherein the design of the pump is such that pressure variations are substantially minimized during the total pump operation.
From the foregoing description, it should be apparent that the prior art type of high pressure fuel injection pump employed must be driven at a timed relationship to the engine output shaft. This requires more expensive drives, such as a positive drive provided for by either a gear transmission or a toothed belt or chain transmission.
It is, therefore, a still further object to this invention to provide a fuel injection system for an engine having a high pressure pump which can be driven so that it does not have to be maintained in timed relationship to the engine output shaft.
The fuel requirements for an engine vary in relation to factors other than merely the speed of the engine. Therefore, with prior art type of constructions that must be driven in timed relationship to the engine output shaft, the driving speed and output of the high pressure pump is always at a fixed relationship to the engine speed. However, the fuel requirements for the engine vary in response to other engine demand than merely speed. For example, under high load conditions, more fuel is required than under low load when the engine is operating at the same speed. Therefore, it has been necessary with prior art constructions to provide a pump that has a capacity that will meet the highest fuel requirements of the engine regardless of the speed at which it is driven.
Although it has been recognized that advantages can be obtained by driving the fuel pump from the engine through a speed change transmission, the variable speed pump drives previously employed all have change speed transmissions that have fixed speed ratios. The reason for this is the necessity to maintain the timed relationship between the engine output shaft and the output pulses of the pump, as aforenoted. Thus, the previously proposed pump driving systems have not been as versatile as desired and have required the use of pumps having larger capacity than is desirable for optimum conditions.
It is, therefore, a still further object of this invention to provide an improved high pressure fuel pump and driving arrangement for an internal combustion engine that permits the use of a continuously variable transmission drive.